Conventionally known methods for an electric connection of a chip-type light emitting diode (LED) and a circuit board are soldering, lead connection, and an electric connection by means of an anisotropic conductive elastic connector. This anisotropic conductive elastic connector is used widely for a small chip-type LED that is difficult to connect electrically by means of soldering or leads. In the recent demands for thin electronic equipment, connections for allowing a decrease in spacing between a chip-type LED and a circuit board are required. And thus, needs for such anisotropic conductive connectors and anisotropic conductive films (ACF) are increased.
However, for decreasing the spacing between the chip-type LED and the circuit board by use of such an anisotropic conductive elastic connector, it is desirable in general that the connector is thin, or the connector is small in the height direction or its energization direction. Though an anisotropic conductive elastic connector satisfying such conditions is as thin as about 0.5 mm, such a connector is difficult to handle, and operations for mounting the connector on electrodes will be quite difficult.
When the thickness of the anisotropic conductive elastic connector is set to be 0.2 mm or less for decreasing the spacing between the chip-type LED and the circuit board to be less than 0.5 mm, the strength of the connector will deteriorate considerably, so that it will be cracked easily when pinched with tweezers or parts-feeders.
Even though the elastic connector serves to decrease the spacing between the chip-type LED and the circuit board, the use of the connector necessarily will increase the number of the components or members in comparison with conventional technique using solder. This is not desirable in view of recent electronic equipment designed for decreasing the numbers of the components.
The chip-type LED and the circuit board will be deformed easily due to impact resilience caused by the sandwiching when an elastic connector is inserted and sandwiched between a chip-type LED and a circuit board for an electric connection of the electrodes, because both the LED and the circuit board are thin and light-weight. As a result, surfaces of the elastic connector in contact with the circuit board can be applied with uniform pressure. In this case, the contact between the conductor of the elastic connector and the electric circuit of the chip-type LED will be insufficient. At worst, the electric circuit may lose its operability.
Thermocompression bonding by use of ACF enables automation in mounting on a circuit board, and thus it allows setting of the spacing between the chip-type LED and a circuit board to be at most several tens of μm. However, a facility for applying heat and pressure will be indispensable. Moreover, heat and pressure should be applied uniformly on the entire surfaces to be bonded so as to provide secure conductivity and adhesion. For such reasons, the method is suitable for mounting electrodes with a flat surface, e.g., connection of electrode terminals on a liquid crystal panel and a flexible printed circuit (FPC) board. However, it is difficult to apply heat and pressure uniformly on respective chip-type LEDs in the case of printed circuit boards on which various chip-type LEDs are mounted, making mounting difficult.
Moreover, it is considerably difficult to peel the LED after the connection in the cases of soldering and AFCs. For example, when any defect is found in an expensive unit of electronic parts such as a semiconductor and a resistor, the whole unit must be discarded even if many chip-type LEDs in the unit have no fault, since the unit cannot be repaired.